It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)

"Intelligence" is a term with many definitions and interpretations. It's difficult enough to measure in humans let alone other animals. Large brains are traditionally associated with greater intelligence, and the brain of the adult bottlenose dolphin is about 25% heavier than the average adult human brain. Generally though, larger mammals tend to have larger brains, and so a more accurate estimate of brain power comes from the ratio of brain size to body size - the "encephalisation quotient" (EQ). While river dolphins have an EQ of 1.5, some dolphins have EQs that are more than double those of our closest relatives: gorillas have 1.76, chimpanzees 2.48, bottlenose dolphins 5.6. The bottlenose's EQ is surpassed only by a human's, which measures 7.4 (Australopithecines - hominids that lived around 4m years ago - fall within the dolphin range: 3.25-4.72). But we don't know enough about the workings of the brain to be sure of what these anatomical measurements truly represent. Today, most scientists share the view that it is behaviour, not structure, that must be the measure of intelligence within a species.Guardian Unlimited | Life | Deep thinkers